Microstructure-dependent oxidation behavior of Ni-Al single-crystal alloys

Abstract

The effect of the γ′+γ two-phase structure on the oxidation behaviors of Ni-Al single-crystal alloys at 650 °C was investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction and Auger electron spectroscopy. In the initial oxidation stage, the oxidation behavior is primarily determined by the growth pattern of oxides in the γ channel. The outward convex NiO was formed in unprotected wide γ channels. And Ni-Al spinel oxide provides a great number of short-circuit paths, accelerating the inward diffusion of oxygen and outward diffusion of Ni. In the late stage of oxidation, the elongated internal oxide in the large γ′ phase contributes to the diffusion of oxygen along the oxide/metal interface. Consequently, the Ni-Al single-crystal alloy with wide γ channels and large γ′ precipitates exhibited poor oxidation performance.